Technical Field
The present disclosure relates to an R-2R ladder resistor circuit, a ladder resistor type D/A conversion circuit, and a semiconductor device.
Related Art
A digital/analog (D/A) conversion circuit, provided with an R-2R ladder resistor circuit, has been widely known. The R-2R ladder resistor circuit is a circuit in which a resistance element with a resistance value R and a resistance element with a resistance value 2R are connected in a ladder shape (for example, see Japanese Patent Application Laid-Open (JP-A) No. S59-181821).
FIG. 4 illustrates an example of a conventional D/A conversion circuit 100. As illustrated in FIG. 4, the D/A conversion circuit 100 is a ladder resistor type D/A conversion circuit including an R-2R ladder resistor circuit 102, and is provided with a reference potential input terminal TREF, bit signal input terminals T-1 to T-N, an operational amplifier A1, and an output terminal Tout.
The reference potential input terminal TREF is connected to a reference potential VREF. Respective bits BIT-1(MSB) to BIT-N(LSB) of a digital signal, which is defined by an N-bit, are input to the bit signal input terminals T-1 to T-N. Here, the MSB indicates the most significant bit, and the LSB indicates the least significant bit.
Resistance elements RB-1 to RB-N−1) and RA-(N+1) are connected in series in the R-2R ladder resistor circuit 102, the resistance element RB-1 is connected to the reference potential input terminal TREF, and the resistance element RA-(N+1) is connected to a ground potential. Each end of resistance elements RA-1 to RA-N is connected to each connection point among the resistance elements RB-1 to RB-(N−1) and RA-(N+1) connected in series, and each other end of the resistance elements RA-1 to RA-N is connected to each movable contact a of switches S-1 to S-N corresponding thereto. Each fixed contact b of the switches S-1 to S-N is connected commonly to an inverting input terminal of the operational amplifier A1, and the other fixed contacts c are connected to the ground potential. Further, an output terminal of the operational amplifier A1 is connected to the inverting input terminal of the operational amplifier A1 via a feedback resistance element Rf.
Here, each resistance value of the resistance elements RA-1 to RA-(N+1) is set to 20 kΩ, and each resistance value of the resistance elements RB-1 to RB-(N−1) and Rf is set to 10 kΩ.
However, in the R-2R ladder resistor circuit 102, the fixed contact b is directly connected to the operational amplifier A1, and thus, a feed through noise, generated in the switches S-1 to S-N in a case in which the switches S-1 to S-N operate, may degrad an output characteristic of the D/A conversion circuit 100. In addition, in a case in which the ground potential is changed to a reference potential as another potential, the reference potential is influenced by the feedthrough noise, since the fixed contact c is also directly connected to the ground potential, and as a result, the output characteristic of the D/A conversion circuit 100 may be degraded. In addition, in a case in which the reference potential is shared with another circuits different from the D/A conversion circuit 100, the other circuits, which commonly uses the reference potential, may also be influenced by the feedthrough noise.